Wireless Tracking System And Method With Multipath Error Mitigation

ABSTRACT

A system ( 50 ) and method ( 300 ) for providing multipath error mitigation for real-time wireless tracking of an object ( 100 ) is disclosed herein. A plurality of sensor readings are obtained from a tag ( 60 ) attached to an object ( 100 ) within an indoor facility ( 70 ). A plurality of reading sets are generated and sorted by zones. A zone with the highest average reading is preferably selected and the location of the object ( 100 ) is calculated based on the selected zone readings. In this manner, faulty position readings are eliminated from the location calculation thereby allowing for more accurate tracking of the object ( 100 ) within the indoor facility ( 70 ).

CROSS REFERENCES TO RELATED APPLICATIONS

The Present Application is a divisional application of U.S. patentapplication Ser. No. 11/672,047, filed on Feb. 7, 2007, which is aContinuation-In-Part Application of U.S. patent application Ser. No.10/968,814, filed on Oct. 18, 2004, now U.S. Pat. No. 7,312,752, whichclaims priority to U.S. Provisional Application No. 60/572,690, filed onMay 19, 2004, now abandoned, U.S. Provisional Application No.60/528,052, filed on Dec. 9, 2003, now abandoned, and U.S. ProvisionalApplication No. 60/513,784, filed on Oct. 22, 2003, now abandoned.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is related to wireless tracking systems andmethods. More specifically, the present invention relates to a systemand method for mitigating multipath errors associated with the wirelesstracking of objects.

2. Description of Related Art

The ability to quickly determine the location of objects located withina facility is becoming a necessity of life. To the uninformed observer,the placement of transponders, also known as tags, on numerousnon-stationary objects whether in an office or home would appear to bean unnecessary use of resources. However, the uninformed observer failsto appreciate the complexity of modern life and the desire forefficiency, whether at the office or home.

For example, in a typical hospital there are numerous shifts ofemployees utilizing the same equipment. When a new shift arrives theability to quickly locate medical equipment not only results in a moreefficient use of resources, but also can result in averting a medicalemergency. Thus, the tracking of medical equipment in a hospital isbecoming a standard practice.

The tracking of objects in other facilities is rapidly becoming a meansof achieving greater efficiency. A typical radio frequencyidentification system includes at least multiple tagged objects, each ofwhich transmits a signal, multiple receivers for receiving thetransmissions from the tagged objects, and a processing means foranalyzing the transmissions to determine the locations of the taggedobjects within a predetermined environment. One exemplary methodtriangulates the strongest received signals to determine the location ofa tagged object. This method is based on the assumption that thereceivers with the strongest received signals are the ones locatedclosest to the tagged object. However, such an assumption is sometimeserroneous due to common environmental obstacles. Multipath effects canresult in a further located receiver having a stronger signal from atagged object than a more proximate receiver to the tagged object, whichresult in a mistaken location determination.

Tekinay, U.S. Pat. No. 6,259,894 for a Method For Improved Line-Of-SightSignal Detection Using RF Model Parameters, discloses a method forreducing time-shift due to multipathing for a RF signal in an RFenvironment.

Close, U.S. Pat. No. 3,869,673 for a Method And Apparatus For MeasuringMultipath Distortion, discloses a method for indicating multipathdistortion in a received signal.

Lennen, U.S. Pat. No. 5,402,450 for a Signal Timing Synchronizer,discloses a method and apparatus for reducing the effects of multipathinduced distortions on the accuracy of detecting the time of arrival ofa received signal.

Fortune et al., U.S. Pat. No. 5,450,615 for a Prediction Of IndoorElectromagnetic Wave Propagation For Wireless Indoor Systems, disclosestechniques for predicting RF propagation within a structure.

The prior art has yet to resolve mistaken location calculations based onmultipath effects.

BRIEF SUMMARY OF THE INVENTION

One aspect of the present invention is a method for determining areal-time location of an object within an indoor facility. The methodbegins with obtaining a plurality of sensor readings from a transponderattached to the object. Next, a reading set is generated from theplurality of sensor readings. The reading set is then sorted by aplurality of physical regions. Then, a first physical region is selectedfrom the plurality of physical regions. The first physical region iscomposed of a first plurality of sensor readings that have the highestaverage signal strength. Next, the first plurality of sensor readings issorted into a second plurality of sensor readings. Each of the secondplurality of sensor readings corresponds to sensor located in a zonewithin the first physical region. A selected zone having the highestaverage reading is then selected. Next, a real-time location of theobject is calculated using only the second plurality of sensor readingsthat correspond to the selected zone.

Each sensor reading preferably comprises a signal strength, linkquality, time and identification of the transponder. The method mayfurther comprise displaying the real-time location of the object on agraphical user interface. The method may also include comparing thecalculated real-time location of the object to a previously calculatedlocation for the object. The method may include monitoring the motionstate of the object to confirm movement of the object from thepreviously calculated location to the real-time location. In a preferredembodiment, the indoor facility is a hospital, with each of theplurality of physical regions being a floor of the hospital, and theselected zone being a room on a floor of the hospital. The plurality ofsensor readings of the reading set preferably comprises from eight tothirty sensor readings for the transponder, and each sensor readingoriginates from a single stationary sensor positioned within the indoorfacility. Each sensor reading is preferably a radio frequencytransmission from the transponder. The step of obtaining a plurality ofsensor readings from the transponder attached to the object preferablycomprises, transmitting a radio frequency transmission from thetransponder, the radio frequency transmission comprising a signalstrength, link quality, time of transmission and identification of thetransponder, receiving the radio frequency transmission at a pluralityof stationary sensors positioned within the indoor facility, andtransmitting the signal strength, the link quality, the time oftransmission and the identification of the transponder from each of theplurality of stationary sensors to a server for processing.

Another object of the present invention is a system for providingreal-time location information for a plurality of non-stationary objectswithin an indoor facility. The system includes a plurality of sensors, aplurality of transponders and a processing means. Each of the stationarysensors is positioned within the indoor facility. Each of thetransponders is attached to one of the non-stationary objects. Each ofthe transponders has means for wirelessly transmitting to each of thestationary sensors transponder-specific data. The processing meansprocesses the transponder-specific data to obtain a real-time readingset for the transponder. The processing means also processes thereal-time reading set to determine a first plurality of sensor readings.The first plurality of sensor readings corresponds to a physical regionwithin the indoor facility having the highest average reading. Theprocessor means then processes the first plurality of sensor readings,which are associated with the selected physical region, to select a zonewithin the physical region having the highest average reading. Theprocessing means then calculates the position of the non-stationaryobject using the sensor readings from the stationary sensors positionedwithin the selected zone of the selected physical region.

The transponder-specific data preferably comprises a signal strength,link quality, time and identification of the transponder. In a preferredembodiment, the indoor facility is a hospital with the physical regionpreferably a floor of the hospital, and the selected zone is a room on afloor of the hospital. The processing means is preferably a server incommunication with the plurality of stationary sensors through anetwork. Each transponder preferably transmits a radio frequencytransmission of approximately 2.48 gigahertz, and each stationary sensorpreferably communicates utilizing a 802.15.4 protocol. The system mayfurther comprise means for eliminating those sensor readings notassociated with (i.e., located within) the selected zone.

Another aspect of the present invention is a method for determining alocation of an object within a predetermined environment. The methodbegins with transmitting a plurality of radio frequency signals for awireless tracking device to a positioning engine. The wireless trackingdevice is attached to the object and each of the radio frequency signalscorresponds to a fixed signal transmitter within the environment. Eachradio frequency signal is processed to determine the location of therespective fixed signal transmitter. A probable region of the object isdetermined based on the location of a majority of the fixed signaltransmitters for the plurality of radio frequency signals. The radiofrequency signals that correspond to fixed signal transmitters locatedoutside of the probable region of the object are eliminated from thelocation determination. The position of the object within thepredetermined environment is calculated using only the radio frequencysignals that correspond to fixed signal transmitters located within theprobable region of the object.

The predetermined environment is preferably a hospital, and the probableregion of the object is preferably a room in the hospital. The step oftransmitting a plurality of radio frequency signals for a wirelesstracking device to a positioning engine preferably comprisestransmitting radio frequency signals from the wireless tracking device,each radio frequency signal comprising a signal strength, link quality,time of transmission and identification of the transponder, receivingthe radio frequency signals at a plurality of stationary sensorspositioned within the predetermined environment, and transmitting thesignal strength, the link quality, the time of transmission and theidentification of the wireless tracking device from each of theplurality of stationary sensors to a server for processing.

Yet another aspect of the present invention is a system for providingreal-time location information for a plurality of non-stationary objectswithin an indoor facility. The system includes a mapped space and aprocessor. The mapped space is of a physical environment of the indoorfacility. The processor includes means for updating the mapped space inresponse to received measurements of the physical environment from oneor more stationary sensors located within the indoor facility, means forgenerating a plurality of location hypotheses for a non-stationaryobject within the physical environment, at least one of the locationhypotheses computed in response to measurement received from thenon-stationary object and the mapped space, and means for generating alocation estimate based on one or more of the plurality of locationhypotheses, wherein one or more of the plurality of location hypothesesare selected based on a probability associated respectively therewith.The probability is computed in association with known barriers in thephysical space.

Having briefly described the present invention, the above and furtherobjects, features and advantages thereof will be recognized by thoseskilled in the pertinent art from the following detailed description ofthe invention when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is schematic view of a system of the present invention.

FIG. 2 is a multi-floor view of a facility employing the system of thepresent invention.

FIG. 3 is a floor plan view of a single floor in a facility employingthe system of the present invention.

FIG. 4 is a two-floor view of a facility including a tagged object andsensors of the system of the present invention.

FIG. 5 is a flow chart of a general method of the present invention.

FIG. 6 is a flow chart of a specific method of the present invention.

FIG. 7 is a flow chart of a specific method of the present invention.

FIG. 8 is a flow chart of a single sensor reading input.

DETAILED DESCRIPTION OF THE INVENTION

As shown in FIGS. 1-4, a system is generally designated 50. The system50 is capable of determining real-time location of an object 100 withinan indoor facility 70. The system 50 preferably includes a plurality ofsensors 55, a plurality of bridges 56, a plurality of tags 60 and atleast one server 65. One example of the components of the system 50 isdisclosed in U.S. Pat. No. 7,312,752 for a Wireless Position LocationAnd Tracking System, which is hereby incorporated by reference in itsentirety. A more specific example of the sensors 55 is disclosed in U.S.Pat. No. 7,324,824 for a Plug-In Network Appliance, which is herebyincorporated by reference in its entirety. Another example of a system50 is set forth in U.S. Pat. No. 6,751,455 for a Power-AndBandwidth-Adaptive In-Home Wireless Communications System WithPower-Grid-Powered Agents And Battery-Powered Clients, which is herebyincorporated by reference in its entirety.

The system 50 is preferably employed within an indoor facility 70 suchas a business office, factory, home, hospital and/or government agencybuilding. The system 50 is utilized to track and locate various objectspositioned throughout the facility 70. The tags 60 continuously transmitsignals on a predetermined time cycle, and these signals are received bysensors 55 positioned throughout the facility 70. The sensors 55transmit the data to a bridge 56 for transmission to a server 65. If asensor 55 is unable to transmit to a bridge 56, the sensor may transmitto another sensor 55 in a mesh network-like system for eventualtransmission to a bridge 56. In a preferred embodiment, a transmissionmay be sent from a transmission distance of six sensors 55 from a bridge56. The server 65 preferably continuously receives transmissions fromthe sensors 55 via the bridges 56 concerning the movement of objects 100bearing a tag 60 within the facility 70. The server 65 processes thetransmissions from the sensors 55 and calculates a real-time positionfor each of the objects 100 bearing a tag 60 within the facility 70. Thereal-time location information for each of the objects 100 bearing a tag60 is preferably displayed on an image of a floor plan of the indoorfacility 70, or if the facility 70 has multiple floors, then on thefloor plan images of the floors of the facility 70. The floor plan imagemay be used with a graphical user interface so that an individual of thefacility 70 is able to quickly locate objects 100 within the facility70.

As shown in FIG. 1, the system 50 utilizes sensors 55 to monitor andidentify the real-time position of non-stationary objects bearing orintegrated with tags 60. The sensors 55 a-f preferably wirelesslycommunicate with each other (shown as double arrow lines) and with aserver 65 through a wired connection 66 via at least one bridge 56, suchas disclosed in the above-mentioned U.S. Pat. No. 7,324,824 for aPlug-In Network Appliance. The tags 60 a-c transmit signals (shown asdashed lines) which are received by the sensors 55 a-e, which thentransmit signals to bridges 56 for eventual transmission to a server 65.The server 65 is preferably located on-site at the facility 70. However,the system 50 may also include an off-site server 65, not shown.

Each tag 60 preferably transmits a radio frequency signal ofapproximately 2.48 GigaHertz (“GHz”). The communication format ispreferably IEEE Standard 802.15.4. Those skilled in the pertinent artwill recognize that the tags 60 may operate at various frequencieswithout departing from the scope and spirit of the present invention.

As shown in FIGS. 2-4, the facility 70 is depicted as a hospital. Thefacility 70 has a multitude of floors 75 a-c. An elevator 80 providesaccess between the various floors 75 a, 75 b and 75 c. Each floor 75 a,75 b and 75 c has a multitude of rooms 90 a-i, with each room 90accessible through a door 85. Positioned throughout the facility 70 aresensors 55 a-o for obtaining readings from tags 60 a-d attached to orintegrated into non-stationary objects 100 a, 100 b (see FIGS. 2 and 4).A bridge 56 is also shown for receiving transmissions from the sensors55 for processing by the server 65.

As shown in FIG. 4, the tag 60 a is attached to movable bed 100 apositioned on an upper floor 75 c. The tag 60 a transmits a signal whichis received by sensors 55 a, 55 b and 55 c. If the signal to sensor 55 cis the strongest, then an analysis of the readings from the sensors 55a-c may place the tag 60 a, and thus the movable bed 100 a, at position60′ on the lower floor 75 b. This type of faulty reading would likelyoccur with triangulation. To prevent such a faulty positioning reading,the present invention processes the readings preferably according to oneof the methods illustrated in FIGS. 5-7, which would eliminate thereading from sensor 55 c from the location calculation for movable bed100 a.

A general method 200 of the present invention is illustrated in FIG. 5.At block 202, the sensors 55 of the system 50 generate readings from thetags 60. These single sensor reading inputs 600 are illustrated in FIG.8. As shown in FIG. 8, the inputs preferably include the tagidentification 604, the signal strength 606, the link quality 608 andthe time of the reading 610, which are inputted as a single sensorreading 602. At block 204, a plurality of readings sets are generatedfrom the sensor readings. In a preferred embodiment, each of theplurality of readings sets represents an area of a facility 70. At block206, the readings are further sorted by a particular zone of thefacility 70 thereby eliminating readings that may lead to an incorrectlocation. In a preferred embodiment, a zone is a subset of an area. Atblock 208, the zone with the highest average reading is selected forcalculation of the position of the object 100, again eliminatingreadings that may lead to an incorrect reading. At block 210, thelocation of the object 100 is calculated based on the readings from theselected zone.

A more specific method 300 of the present invention is set forth in FIG.6. At block 302, the sensors 55 of the system 50 generate readings fromthe tags 60. As discussed above, the single sensor reading inputs 600are illustrated in FIG. 8. At block 304, a reading set is generated forreadings from a single tag 60. The generation of the reading set istypically in response to an inquiry from a user of the system 50 insearch of an object 100 bearing tag 60. At decision block 306, theserver 65 determines if there is sufficient data to proceed with thelocation analysis. If there is insufficient data, the method isrestarted at block 302. If there is sufficient data, then the methodproceeds to block 308. At block 308, the reading sets are separated byfloor 75 of the facility 70. At block 310, the floor 75 with the highestaverage reading set is selected for further processing. At block 312,the readings for the selected floor are sorted by zones. Each zone mayrepresent any physical boundary on the selected floor 75 of the facility70. Preferably, the zones represent a room 90, station 95 or othereasily determined physical location. At block 314, the zone with thehighest average reading is selected. At block 316, the location of theobject 100 is calculated based on the readings from the selected zone.At block 318, the location is inputted to the location database fordissemination to users of the system to locate the object 100.

An even more specific method 400 of the present invention is set forthin FIG. 7. At block 402, the sensors 55 of the system 50 generatereadings from the tags 60. As discussed above, the single sensor readinginputs 600 are illustrated in FIG. 8. At block 404, a reading set isgenerated for readings from a single tag 60. The generation of thereading set is typically in response to an inquiry from a user of thesystem 50 in search of an object 100 bearing tag 60. At decision block406, the server 65 determines if there is sufficient data to proceedwith the location analysis. If there is insufficient data, the method isrestarted at block 402. If there is sufficient data, then the methodproceeds to block 408. At block 408, the reading sets are separated byfloor 75 of the facility 70. At block 410, the floor 75 with the highestaverage reading set is selected for further processing. At block 412,the readings for the selected floor are sorted by zones. Each zone mayrepresent any physical boundary on the selected floor 75 of the facility70. Preferably, the zones represent a room 90, station 95 or othereasily determined physical location. At block 414, the zone with thehighest average reading is selected. At block 416, the location of theobject 100 is calculated based on the readings from the selected zone.

At decision block 418, the server 65 inquires if the new calculatedlocation is consistent with available data for the object 100. Theavailable data includes the motion sensor state of the object 100 whichis tracked at block 424. If the motion sensor has not detected a motionthreshold of the object 100, then that is one indication that the newcalculated location is in error. However, if the motion sensor hasdetected movement (a motion threshold) of the object 100, then that isone indication that the new calculated location is correct. Additionaldata for the decision block 418 includes recently calculated locationsfor the object 100 which are available from database 426. Yet furtherdata available for decision block 418 is data from the possiblehypotheses database 428. The possible hypotheses database includes datasuch as the timing between the last calculated location and the newcalculated location. If the object 100 has moved one end of the facility70 to another end of the facility 70 within seconds, then the newcalculated location may be in error. If the response to decision block418 is yes, then at block 420 the location is inputted to the locationdatabase for dissemination to users of the system to locate the object100. If the response to decision block 418 is no, then the newcalculated location is held as an unproven hypothesis at block 422.

The following example illustrates the information that is utilized andeliminated in practicing the present invention.

TABLE ONE Sensor Signal Strength Link Sensor Location # dB Quality Time(floor/region) 1 −95 −95 Sep. 14, 2006 5/B 11:22:35 2 −10 −10 Sep. 14,2006 4/C 11:22:35 3 −20 −20 Sep. 14, 2006 4/C 11:22:36 4 −25 −25 Sep.14, 2006 4/C 11:22:35 5 −40 −40 Sep. 14, 2006 4/C 11:22:36 6 −50 −50Sep. 14, 2006 4/C 11:22:36 7 −70 −70 Sep. 14, 2006 4/D 11:22:36 8 −80−80 Sep. 14, 2006 4/D 11:22:36 9 −90 −90 Sep. 14, 2006 4/E 11:22:37 10−95 −95 Sep. 14, 2006 4/E 11:22:37

TABLE TWO Floor Average Reading per Floor 2 N/A 3 −120 4 −30 5 −85

TABLE THREE Region Peaks Average Reading per Region C −20 −20 D −10 −70E −70 −95

As shown in Table One, the signal strength from each tag 60 is provideddBm with a full strength value of zero, which is a ratio of powerrelative to 1 milli-Watt. The Link Quality value is provided as asimilar value as the signal strength. The time is a date stamp of thetime and date that the signal is received by the sensor 55. The sensorlocation is preferably a floor and region on the floor. In a preferredembodiment, the regions on the floors overlap each other. The regionsare preferably determined based on the facility 70.

In Table One, ten readings from sensors 55 positioned on various floorsof the facility 70. Each of the readings is transmitted from a singletag 60 to the sensors 60. The sensors 60 transmit the data from the tag60 to the server 65 via bridges 56. The server 65 uses the data tocalculate the location of the object 100 as discussed. The sensorlocation may also be provided in terms of a X-Y position which is basedon a floor plan image of each floor of the facility 70. The X-Y positionmay be based on the pixel location on the image of the floor plan.

The average reading from all of the sensors 55 on each floor is providedin Table Two. More specifically, if the fifth floor has ten sensors 55that each received a signal from a specific tag 60, then the readingsfrom those ten sensors 55 are averaged to obtain the average reading perfloor value provided in Table Two. The readings from the floor with thehighest value are then further processed to determine the location ofthe object 100. The readings from the sensors 55 on the other floors areeliminated from the calculation for the location of the object 100.

The average reading from all of the sensors 55 in each region on theselected floor is provided in Table Three. As mentioned above, theregions preferably overlap so that a single sensor 55 may be in two ormore regions, and used in the average reading for both regions. The peakreading for each region is also set forth in Table Three. In analternative embodiment, if the peak reading exceeds a threshold, thenthat region is selected even if the average readings for that region areless than another region. In calculating the location of the object 100,the highest readings within a selected region are used for thecalculation. The number of readings used preferably ranges from 2 to 10,and is most preferably 3 to 5. The more readings used in thecalculation, the longer the processing time for the calculation. Thus,using 10 readings may provide a more accurate location, however, theprocessing time will be longer than using 3 readings. In a preferredembodiment, a radial basis function is utilized in calculating thelocation of the object 100. The location of the object 100 is preferablyconveyed as an XY coordinate on an floor plan image of the facility 70.

From the foregoing it is believed that those skilled in the pertinentart will recognize the meritorious advancement of this invention andwill readily understand that while the present invention has beendescribed in association with a preferred embodiment thereof, and otherembodiments illustrated in the accompanying drawings, numerous changesmodification and substitutions of equivalents may be made thereinwithout departing from the spirit and scope of this invention which isintended to be unlimited by the foregoing except as may appear in thefollowing appended claim. Therefore, the embodiments of the invention inwhich an exclusive property or privilege is claimed are defined in thefollowing appended claims.

1. A method for determining a location of an object within apredetermined environment, the method comprising: transmitting aplurality of radiofrequency signals for a wireless tracking device to apositioning engine, each of the plurality of radiofrequency signalscorresponding to a signal transmitter within the environment; processingeach of the plurality of radiofrequency signals to determine thelocation of the signal transmitter for each of the plurality ofradiofrequency signals; determining a probable region of the objectbased on the location of a of the signal transmitter for each of theplurality of radiofrequency signals; weighting any of the plurality ofradiofrequency signals corresponding from a fixed signal transmitterlocated outside of the probable region of the object; and calculatingthe position of the object within the predetermined environment usingonly the plurality of radiofrequency signals corresponding to a fixedsignal transmitter within the probable region of the object.
 2. Themethod according to claim 1 wherein the predetermined environment is ahospital and the probable region of the object is a room in thehospital.
 3. The method according to claim 1 wherein transmitting aplurality of radio frequency signals for a wireless tracking device to apositioning engine comprises: transmitting radio frequency signals fromthe wireless tracking device comprising signal strength, link quality,time of transmission and identification of the wireless tracking device;receiving the radio frequency signals at a plurality of stationarysensors positioned within the predetermined environment; andtransmitting the signal strength, the link quality, the time oftransmission and the identification of the wireless tracking device fromeach of the plurality of stationary sensors to a server for processing.4. The method according to claim 1 further comprising displaying thereal-time location of the object on a graphical user interface.
 5. Themethod according to claim 1 further comprising comparing the calculatedlocation of the object within the predetermined environment to apreviously calculated location for the object.
 6. The method accordingto claim 5 further comprising monitoring the motion state of the objectto confirm movement of the object from the previously calculatedlocation to the location of the object within the predeterminedenvironment.
 7. A system for providing real-time location informationfor a plurality of non-stationary objects within an indoor facility, thesystem comprising: a mapped space of a physical environment of theindoor facility; and a processor comprising means for updating themapped space in response to received measurements of the physicalenvironment from one or more stationary sensors located within theindoor facility, means for generating a plurality of location hypothesesfor a non-stationary object within the physical environment, at leastone of the location hypotheses computed in response to measurementreceived from the non-stationary object and the mapped space, and meansfor generating a location estimate based on one or more of the pluralityof location hypotheses, wherein one or more of the plurality of locationhypotheses are selected based on a probability associated respectivelytherewith, and wherein a probability is computed in association with aplurality of known barriers in the physical space.
 8. The systemaccording to claim 7 wherein the indoor facility is a hospital.
 9. Thesystem according to claim 7 wherein the measurement from the object isgenerated from a radiofrequency signal from a tag.
 10. The systemaccording to claim 9 wherein the radiofrequency signal from a tagcomprises signal strength, link quality, time and identification of thetag.
 11. The system according to claim 10 wherein the processor islocated at a remote server in communication with the plurality ofstationary sensors through at least one bridge device.
 12. The systemaccording to claim 9 wherein the tag transmits a radiofrequency signalof approximately 2.48 GigaHertz, and each of the plurality of stationarysensors communicates utilizing a 802.15.4 protocol.
 13. A system forproviding real-time location information for a plurality ofnon-stationary objects within an indoor facility, the system comprising:a plurality of stationary sensors, each of the plurality of stationarysensors positioned within the indoor facility; a plurality of tags, eachof the plurality of tags attached to one of the plurality ofnon-stationary objects, each of the plurality of tags having means forwirelessly transmitting to each of the plurality of stationary sensorstag specific data; a mapped space of a physical environment of theindoor facility; a processor comprising means for updating the mappedspace in response to received measurements of the physical environmentfrom one or more stationary sensors located within the indoor facility,means for generating a plurality of location hypotheses for each of theplurality of non-stationary objects located within the physicalenvironment, at least one of the location hypotheses computed inresponse to measurement received from a non-stationary object of theplurality of non-stationary objects and the mapped space, and means forgenerating a location estimate based on one or more of the plurality oflocation hypotheses, wherein one or more of the plurality of locationhypotheses are selected based on a probability associated respectivelytherewith, and wherein a probability is computed in association with aplurality of known barriers in the physical space.
 14. The systemaccording to claim 13 wherein the indoor facility is a hospital.
 15. Thesystem according to claim 13 wherein the measurement from the object isgenerated from a radiofrequency signal from the tag.
 16. The systemaccording to claim 15 wherein the radiofrequency signal from a tagcomprises signal strength, link quality, time and identification of thetag.
 17. The system according to claim 13 wherein the processor islocated at a remote server in communication with the plurality ofstationary sensors through at least one bridge device.
 18. The systemaccording to claim 15 wherein the tag transmits a radiofrequency signalof approximately 2.48 GigaHertz, and each of the plurality of stationarysensors communicates utilizing a 802.15.4 protocol.
 19. The systemaccording to claim 13 wherein a radial basis function is utilized by theprocessor in generating a location estimate.
 20. The system according toclaim 13 wherein the processor further comprises means for determiningif the calculated location is consistent with a previous location.